Mixing polyurethane components

Hi,
I currently use an IKA high shear homogenizer for mixing PU foam components but I find that it is not very efficient due to the high viscosity of the prepolymer and polyols. I would be interested to know how others mix their PU components.
Kind regards,
Gillian

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Don't know about PUs, but the Hauschild Speedmixer is often used for adhesives.
Regards,         Oliver

heat it up. it will be easier to mix.

You will get better results if you fit a small propeller with a shaft bearing 3 or 4 inclined blades (diameter around 4-6 cm) to a simple power drill fixed on a benchtop stand. Smaller benchtop laboratory mixers are also suitable (e.g. IKA Eurostar, etc.) for small amounts. Various blade shapes and angles are possible, with or without guard rings, like those available as paint mixers. They can be operated at around 2000 rpm (or even 3000 rpm for some drill / variator combinations). The more sophisticated models have an electromagnetic brake to better control short mixing times for reactive products (e.g. Ytron, not described on their website).
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On Thu, 2006-02-23 at 14:30 +0100, infinitum wrote:
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Now admittedly I am not a mixer expert, but high rpms with mixing a high viscosity liquid doesn't sound right to me. I guess right around the propeller it would get mixed, but as there will be little flow in the container (this in contrast with low to medium viscosity liquids, and highly sheer thinning, such as paints). I would go for low rpm, high sheer mixers where the mixing elements move a larger distance and cover the complete container. Please correct me if this intuition is wrong.
Wouter.
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<FONT COLOR="#000000">&gt; Hi,</FONT> <FONT COLOR="#000000">&gt;</FONT> <FONT COLOR="#000000">&gt; I currently use an IKA high shear homogenizer for mixing PU foam</FONT> <FONT COLOR="#000000">&gt; components but I find that it is not very efficient due to the high</FONT> <FONT COLOR="#000000">&gt; viscosity of the prepolymer and polyols. I would be interested to know</FONT> <FONT COLOR="#000000">&gt; how others mix their PU components.</FONT> <FONT COLOR="#000000">&gt;</FONT> <FONT COLOR="#000000">&gt; Kind regards,</FONT> <FONT COLOR="#000000">&gt;</FONT> <FONT COLOR="#000000">&gt; Gillian</FONT> <FONT COLOR="#000000">&gt;</FONT>
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It is often possible to mix foam ingredients in a cup with a spatula (low shear, low rpm) and to get decent quality. Industrial foaming machines (low pressure types) on the other hand, work with high shear/high rpm rotors in a small mixing chamber where all the ingredients are pumped through at a set rate. If you slow down the rotor, you quickly get poor foam. The set-up I proposed is a practical method widely used in laboratories for mixing batchwise, small amounts (up to about 500 g) raw materials up to about 100 Pa.s at room temperature. Maybe I could have added that it helps to move the cup around the mixer while it's on to optimise homogeneity. Foam ingredients are reactive and mixing should be completed before creaming, which may take place within 5-10 seconds. Also traditional high shear mixers with rotor/stator are more difficult to clean.
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GillianH wrote:
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Check out centrifugal mixers- you won't believe how amazing and fast they are for batch mixing high viscosity materials (not good for dispersion, though)...
http://www.thinky.co.jp/english/w-rentaro_e.html